1. Not sure, could be hahniana r a short spined geminispina
2. Yes, I'd say rhodantha, maybe ssp. pringlei or aureiceps
3. First glance, I thought that's not a Mamm its a Parodia. The look of the plant and a hooked golden central (1) didn't ring any bells. It also looks like the growing point is elongating.
4. Could be a karwinskiana.
But not entirely sure.